This invention pertains generally to methods and apparatus for monitoring acoustic emissions, and more particularly to methods and apparatus that identify the source location of such emissions.
Non-destructive methods for testing mechanical components and metal formations formed during the manufacture of such components, such as weld seams, have been employed for a number of years to detect discontinuities that might otherwise affect the reliability of operating components. If it were not for such inspection techniques, flaws could result in mal-functions during use, which are likely to cause substantial and sometimes irreparable damage.
In recent years, acoustic inspection techniques have been developed which have significantly advanced the state of the art. Usually such techniques employ ultrasonic technology in various embodiments that basically rely on externally generated acoustic pulses which are transmitted within the member being inspected. The time of travel of reflected signals are interpreted to identify the presence and the location of flaws. The application of ultrasonic non-destructive testing techniques, however, usually requires elaborate scanning arrangements which are costly and are not normally practical for on-line applications.
Acoustic emission monitoring techniques have also been employed in non-destructive testing applications, however, such procedures have encountered great difficulties in identifying the source locations of flaws in varying geometries of materials. Additionally, such procedures have proved highly susceptable to multiple acoustic emissions occurring within the same time frame that obscure identification of the source location of any particular emission.
The invention described in application Serial No. 556,354, filed Mar. 7, 1975 entitled "Acoustic Emission Monitoring System" by D. M. Romrell addresses many of the problems encountered in applying acoustic emission monitoring techniques as a non-destructive tool for testing weldments. While the invention described in the cited application significantly advances the present state of the art in an application to relatively small identifiable areas of inspection, the procedures and apparatus set forth become cumbersome and expensive when applied to monitoring relatively large surface areas where the zones of suspected flaw formation are not specifically identifiable.
Presently, fault location using acoustic sensors is being pursued as a means of detecting incipient faults in the pressure walls of reactor vessels. While the sensors and signal conditioners are critical components in obtaining dependable performance, the deployment of sensors and the amount of circuitry required to determine fault location are also important considerations. Since acoustic signals in large medias such as reactor pressure vessels are attenuated and protrusions obstruct propagation through some regions, a large number of sensors is needed, for expansive regions such as are encountered on a reactor pressure vessel, without general duplication of functions.
Accordingly, an acoustic monitoring system is desired that will facilitate on-line monitoring of operating components and discriminate against multiple acoustic events. Additionally, such a system is desired that can be expanded with a minimal of circuitry and cost to accommodate an infinite number of sensors in an application to relatively large surface areas.